feat: add DEX job common infrastructure

Add foundational types for DEX job execution:

Constants:
- ErrorAction enum (Ignore, Stop) for error handling strategy

DTOs:
- CheckQueryResult: check query execution result with ReturnValue
- MainQueryResult: main query execution result with ReturnValue

Interfaces:
- ISQLExecutor: abstraction for SQL query execution and DTO mapping

All types include comprehensive XML documentation

ECMJobRunner.Application/Common/Interfaces/ISQLExecutor.cs

@@ -0,0 +1,20 @@
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace ECMJobRunner.Application.Common.Interfaces
+{
+    /// <summary>
+    /// Interface for executing SQL queries and mapping results to DTOs
+    /// </summary>
+    public interface ISQLExecutor
+    {
+        /// <summary>
+        /// Executes a SQL query and maps the result to the specified type
+        /// </summary>
+        /// <typeparam name="TResult">The type to map the query result to</typeparam>
+        /// <param name="sql">The SQL query to execute</param>
+        /// <param name="cancellationToken">Cancellation token</param>
+        /// <returns>The mapped result or null if no result</returns>
+        Task<TResult?> ExecuteQueryAsync<TResult>(string sql, CancellationToken cancellationToken = default);
+    }
+}